Seasonal field energetics and water influx rates of the greater bilby (Macrotis lagotis)

Water and energy requirements of free-living male and female greater bilbie s (Macrotis lagotis) were measured over two summers and two winters on Astr ebla Downs National Park in far south-western Queensland, Australia, by mea ns of the doubly labelled water method. Mean water influx rate of the bilby (mean body mass: summer 928 g; winter 848 g) did not differ between summer (63.1 mL day(-1)) and winter (53.1 mL day(-1)), but mean field metabolic r ate was significantly higher during summer (617.2 kJ day(-1)) than in winte r (480.3 kJ day(-1)). The comparatively low water influx rate of the bilby (significantly lower than that predicted for a 887-g marsupial: P < 0.001) indicated that bilbies have the ability to conserve water in the wild. In c ontrast, field metabolic rate of the bilby did not differ significantly fro m that predicted for a marsupial of its body mass (P = 0.999). Bilbies were able to obtain sufficient food and water to satisfy energy and water requi rements in three out of the four study periods. However, they were in negat ive energy and water balance during one study period, suggesting that they are susceptible to nutrient and water stress. The relatively low body fat s tores of bilbies in the wild also indicate that they are vulnerable to peri ods of low food availability. The metabolic strategies of the bilby are onl y partly suggestive of adaptation to arid conditions.